That article says calendar ageing was the dominant ageing mechanism for batteries in their test vehicle, because said vehicle spent 96% of its life stationary. Unless I'm missing it, the article doesn't put a number figure on the rate of calendar ageing.

Real-world observations suggest batteries are likely to be serviceable for around 20 years, which is around the same lifetime of an average ICE car. Users who can tolerate a much reduced range (which is most of us) can likely extend this even further.